The invention described herein arose in the course of, or under, Contract No. DE-AC08-88NV10617 between the United States Department of Energy and EG&G Energy Measurements, Inc.
This invention relates to a hazardous fluid leak detector apparatus. More particularly, this invention relates to an apparatus which will detect the presence of hazardous fluids by passing a gas from a monitored enclosure through a body of deionized water containing electrodes in series with a power source and an alarm. Any fumes, vapors, or liquids of hazardous fluids, entrained in the gas which enters the deionized water, will cause the water to conduct, to thereby activate the alarm.
In the prior art, testing and monitoring for the presence of certain gases or liquids has been carried out by passing a gas through a liquid in a vessel containing electrodes. These electrodes are then connected to measuring devices which respectively measure voltage generated by the electrodes, or the pH of the liquid, or changes in resistance between the electrodes. Such detection systems are then, in turn, usually connected to visual or audible devices which signal changes in the gas content passing into the liquid.
For example, the monitoring of voltage generation, or voltage changes between electrodes immersed in a liquid through which a gas is passed, is described in Jacobson U.S. Pat. No. 2,156,693; Jacobson et al. U.S. Pat. Nos. 2,795,756 and 2,939,827; Bushman U.S. Pat. No. 4,326,200; and Miyoshi et al. U.S. Pat. No. 4,478,704.
Jacobson U.S. Pat. No. 2,156,693 describes a structure for testing for the presence of a gas using an electrode which is reactive with the gas to be detected. The electrode which is reactive with the gas is partially immersed in an electrolyte such as ammonium hydroxide or ammonium chloride. A second electrode is totally immersed in the electrolyte. When the partially immersed electrode is contacted by the gas to be detected, the reaction between the gas and the electrode causes an EMF to be generated between the two electrodes. The EMF so generated is then measured by means such as a milliammeter and a Wheatstone bridge to determine the concentration of the gas.
Jacobson et al., U.S. Pat. No. 2,795,756 discloses an elaborate electrical control system used to process the signal from a galvanic cell which is used to measure the concentration of gases which pass through the cell.
Jacobson et at. U.S. Pat. No. 2,939,827 describes a Fery type primary galvanic cell used to determine the oxygen content of a gas using a zinc anode, a porous carbon electrode, and an ammonium chloride electrolyte in which depolarization of the cathode depends upon the diffusion of oxygen in the sample mixture through the cathode to the electrode-electrolyte interface, where it oxidizes the hydrogen ions there liberated. The measured electrical energy of the cell is a function of the oxygen concentration in the sample.
Bushman U.S. Pat. No. 4,326,200 describes a device for detecting CO.sub.2 comprising a vessel containing water wherein a layer of ion-exchange resin wetted by the water is sandwiched between air and water-permeable electrode gauze discs. Any CO.sub.2 gas in the ambient atmosphere dissolves in the water and the dissociated ions lower the resistance between the electrodes. The electrodes may be connected to a bridge circuit adjusted to be out of balance at a predetermined CO.sub.2 level; or the electrodes may be formed of dissimilar metals to form a galvanic cell with a measurable output current at a predetermined CO.sub.2 concentration.
Miyoshi et al. U.S. Pat. No. 4,478,704 shows a gas detection device for detecting levels of CO and H.sub.2 using an electrolytic cell containing a working electrode, a reference electrode, and a counter electrode, with a sulfuric or phosphoric acid electrolyte. Voltages changes between the electrodes, indicative of changes in the levels of CO and H.sub.2 passing through the cell, are monitored.
Brooke U.S. Pat. No. 2,934,408 and Hannan et at. U.S. Pat. No. 4,513,280 monitor pH changes in a liquid caused by passing a gas through the liquid. The Brooke patent teaches apparatus for detecting the presence of acetylene in ethylene by passing the ethylene gas through a vessel containing silver nitrate and a buffering agent. Any acetylene in the gas reacts with the silver nitrate to form nitric acid. After the buffering agent is expended, the nitric acid causes the pH to drop. Electrodes in the vessel connected to a pH meter record the drop in pH which activates a valve to shut off the gas flow. A flowmeter records the amount of gas passed into the cell prior to this shut off to permit determination of the concentration of the acetylene in the ethylene gas.
In the Hannan et al. patent, cells are disclosed for detecting CO.sub.2 levels in water based on a reduction in pH in the water. The CO.sub.2 enters the chamber in which the ph is being monitored through a CO.sub.2 permeable membrane.
The above-mentioned Bushman patent also discloses the measurement and monitoring of resistance changes in the liquid, as is also taught in Brizzolara U.S. Pat. No. 3,040,245. In the Brizzolara patent, there is disclosed a gas detector wherein gases from several locations are pumped through tap water in a flask which also contains electrodes. The electrodes are immersed in the tap water and electrically connected to a resistance measuring unit which monitors the changes in conductivity of the water. The resistance monitoring unit, in turn, controls a power supply and a signal. The signal is thereby activated when the gas supplied into the water causes a predetermined change in the conductivity or resistivity of the water.
What all of the above described systems or devices, however, share in common is a detection system, which then, in turn, is coupled to some sort of visual or audible monitoring device or signal. The disclosed detection systems are usually somewhat elaborate and complicated, for example, requiting bridges for measuring small voltages or changes in resistance, etc. In the case of Brizzolara, for example, the electrodes immersed in the liquid to monitor the resistance changes in the liquid, are connected to the grid of an triode vacuum tube, as well as to a grid power supply (C voltage), with the plate of the vacuum tube connected to a B+ voltage and a relay. The contacts of the relay are, in turn, then connected in series with yet another power supply and a signal.
It would, therefore, be desirable to provide a much simpler monitoring device which would require no separate detection system or circuitry, but which could rather be connected directly to a power supply and alarm signal and wherein the liquid used to monitor the presence of gas could be easily replenished, without any need for the recalibration of measuring devices used with the liquid.